1. Field of the Invention
The present invention relates to a non-hydrolytic transparent composite composition having excellent transparency and heat resistance and a low thermal expansion coefficient.
2. Description of Related Art
In general, glass plates have been used as a thin film transistor (TFT) substrate for liquid crystal display (LCD) or organic electroluminescent (EL) display device, color filter substrate, touch screen panel substrate, solar cell substrate, or the like. However, since glass plate is not flexible, is fragile and is heavy, it is not suitable for providing low-weight devices. Recently, due to such shortcomings, many studies have been conducted about plastic substrates including optical polymers or various composite resin materials as materials substituting for glass substrates.
Polymers used in the above-mentioned plastic substrates include polyethylene terephthalate (PET), polyether sulfone (PES), polyethylene naphthalate (PEN), polyarylate (PAR), polycarbonate (PC), polyimide (PI), etc. However, such conventional plastic materials have a severe shortcoming in that they have a high thermal expansion coefficient. While glass generally has a thermal expansion coefficient of approximately several ppm/° C., the plastics have a relatively high thermal expansion coefficient of at least several tens [of] ppm/° C. The problem related with such a high thermal expansion coefficient may cause degradation of dimensional stability during the fabrication of a device, such as TFT. Moreover, because most plastic materials specifically show a rapid change in thermal expansion coefficient before and after the glass transition temperatures, they cause problems, such as bending or disconnection, during the fabrication of a device. Such problems result in an additional problem in that plastic substrates are used within a limited range of process temperatures, and thus the device is fabricated at a reduced temperature.
In the case of a PI substrate having a relatively low thermal expansion coefficient and a high glass transition temperature, PI has [a] very low transparency as determined by a light transmission of 30-60%, and shows a high birefringence, and thus is not suitable for a substrate material substituting for glass.
More recently, many studies have been conducted to develop composite resins that solve the above problems of plastic materials.
Particularly, such composite resin compositions include: a composition including a cycloaliphatic epoxy resin, an acid anhydride curing agent and a curing catalyst as disclosed in Japanese Laid-Open Patent No. Hei6-337408; a composition including an cycloaliphatic epoxy resin, a carboxylic [acid group-containing] acid anhydride curing agent and a curing catalyst as disclosed in Japanese Laid-Open Patent No. 200159015; a composition including a styrene-methacrylate copolymer as disclosed in Japanese Laid-Open Patent No. Sho54-24933; a composition including an acrylic resin and a styrene-acrylonitrile copolymer as disclosed in Japanese Published Patent No. Hei6-94523; a composition including an N-substituted maleimide-olefin copolymer as disclosed in Japanese Laid-Open Patent No. Hei5-140367; or the like. However, substrates using such existing composite resins may cause degradation of transparency due to a yellowing phenomenon and have difficulties in adjusting the refractive index of the resin to the refractive index of the glass filler. In addition, the substrates still have a high thermal expansion coefficient to provide [reliable] dimensional stability and show insufficient heat resistance. Therefore, substrate materials that may substitute for glass preferably have a low thermal expansion coefficient, excellent optical transparency and heat resistance, and more preferably have no glass transition behavior in a range of temperatures where a device is fabricated.
More recently, in addition to the above-mentioned conventional plastic materials and composite resins, siloxane-based organic resins have been studied as materials for display and optical devices. For example, Japanese Laid-Open Patent Nos. 2005-285778, 2005-285779 and 2005-285780 disclose a composition including a silicone resin and glass cross. In addition, Japanese Laid-Open Patent No. 2004-109768 discloses a resin composition including a hydrolytic condensation product between metal alkoxides. However, such compositions are insufficient for providing substrates satisfying mechanical properties, transparency and flexibility at the same time.
Further, although there is no clear factor found to date, hydrolytic condensation using water and a solvent for carrying out condensation of a silicone resin still have problems in that it causes poor resin stability due to a trace amount of water remaining after the crosslinking of the resin, and it results in the shrinking of the resin due to the use of a solvent.
As materials capable of solving the above-mentioned problems, Korean Laid-Open Patent Nos. 10-0614976 and 10-0569220 disclose compositions including organic/inorganic hybrid oligomers having a functional organic group on the outside thereof. Such compositions are obtained by non-hydrolytic condensation with no water added during the condensation. The nanohybrid polymers obtained using such compositions alone have flexibility, light transmission, wear resistance, heat resistance and insulation property. However, such polymers still have a high thermal expansion coefficient and limited mechanical strength. Therefore, they are not suitable as substrate materials substituting for the existing glass plate.